using System; 
using System.Collections.Generic;
using System.Text;

namespace System.Data.Linq.SqlClient 
{
    /// <summary> 
    /// Find referenced Aliases within a node. 
    /// </summary>
    internal static class SqlAliasesReferenced 
    {
        /// <summary>
        /// Private visitor which walks the tree and looks for referenced aliases.
        /// </summary> 
        private class Visitor : SqlVisitor {
            internal IEnumerable<SqlAlias> aliases; 
            internal bool referencesAnyMatchingAliases = false; 

            internal override SqlNode Visit(SqlNode node) { 
                // Short-circuit when the answer is alreading known
                if (this.referencesAnyMatchingAliases) {
                    return node;
                } 
                return base.Visit(node);
            } 
 
            internal SqlAlias VisitAliasConsumed(SqlAlias a) {
                if (a == null) 
                    return a;

                bool match = false;
                foreach (SqlAlias alias in aliases) 
                    if (alias == a) {
                        match = true; 
                        break; 
                    }
 
                if (match) {
                    this.referencesAnyMatchingAliases = true;
                }
 
                return a;
            } 
 
            internal override SqlExpression VisitColumn(SqlColumn col) {
                VisitAliasConsumed(col.Alias); 
                VisitExpression(col.Expression);
                return col;
            }
 
            internal override SqlExpression VisitColumnRef(SqlColumnRef cref) {
                VisitAliasConsumed(cref.Column.Alias); 
                VisitExpression(cref.Column.Expression); 
                return cref;
            } 
        }

        /// <summary>
        /// Returns true iff the given node references any aliases the list of 'aliases'. 
        /// </summary>
        internal static bool ReferencesAny(SqlNode node, IEnumerable<SqlAlias> aliases) { 
            Visitor visitor = new Visitor(); 
            visitor.aliases = aliases;
            visitor.Visit(node); 
            return visitor.referencesAnyMatchingAliases;
        }
    }
} 

// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.